This proposal concerns two fundamental aspects of development: the creations of cell diversity and the directed movements of differentiating cells. The experimental organism is the simple eukaryote Dictyostelium discoideum. During its life cycle, two precursor cell types diverge from undifferentiated amoebae. The differentiating cells move, or sort out, resulting in spatially distinct spore and stalk "tissues." The technique of density gradient centrifugation provides a means of separating the precursor populations. I shall compare the protein and messenger RNA composition of pre-spore and pre-stalk cells. Differences will also be sought with respect to molecules residing on the cell surface and those previously implicated in slime mold chemotaxis and early differentiation. The effects of possible physiological regulators on the relative proportions of the two cell types will be investigated. By mixing together labelled amoebae of different developmental tendencies, the sorting out of like cells within the aggregate can be observed. In this way the timing and the developmental significance of sorting out will be explored. As an adjunct to these studies, the transformation of Dictyostelium mutants with wild type slime mold DNA has recently been undertaken. The successful development of this technique should have applications to parasexual genetic analysis in Dictyostelium and to the molecular investigation of particular mutations.